US20110081981A1 - Speed detector and swing tool having the same - Google Patents

Abstract

A speed detector includes: a pressure sensor including a pitot tube attached to a moving body in a state in which an air inlet hole is directed toward a direction of a movement of the moving body, a diaphragm having a pressure receiving surface displaced by pressure, and a pressure-sensitive section adapted to receive force caused by the displacement to detect the pressure, the pressure sensor being disposed to the moving body and detecting the pressure caused in the pitot tube; and an operation section adapted to detect a speed of the moving body based on the difference between the pressure at rest and the pressure in movement of the moving body, wherein the pressure sensor is disposed so that a normal line of the pressure receiving surface becomes perpendicular to the direction of the movement.

Description

BACKGROUND
• 1. Technical Field
• The present invention relates to a speed detector, and in particular to a speed detector composed mainly of a pitot tube and a pressure sensor, and attached to a SWING tool, and the SWING tool attached with the speed sensor.
• 2. Related Art
• In ball sports such as golf, baseball, or tennis, practice swings and stroke practices with a golf club, a bat, or a tennis racket are extremely important for upskilling, and therefore, sport persons and athletes practice with practice swings night and day. Further, in the practice with practice swings, how the stroke skill is improved is often determined by objectively measuring the speed of the swing.
• FIGS. 7A and 7B show a speed measuring device according to JP-A-63-105777 (Document 1) as a first related-art example. FIG. 7A is a diagram showing a form of use of the speed measuring device, and FIG. 7B is a detail diagram of the speed measuring device. InDocument 1, there is disclosed aspeed measuring device 100 having apitot tube 104, apressure sensor 106 for detecting the pressure generated in thepitot tube 104, anarithmetic section 116 for performing an operation on the signal of thepressure sensor 106 to thereby obtain a swing speed, and adisplay section 118 for displaying the result of the arithmetic operation, and incorporated in a stroke tool (a bat) 102.
• In the stroke tool according toDocument 1, when swinging the stroke tool, a relative speed movement occurs between the air and the stroke tool, and as a result, from a viewpoint of the stroke tool, the air flows at the same speed as the movement speed of the stroke tool in the opposite direction to the direction thereof. It is attempted that the swing speed of the stroke tool is obtained by measuring the flow rate of the air. Further, inDocument 1, thepitot tube 104 is used for measuring the flow rate of the air. In the case of attaching thepitot tube 104 to the stroke tool, when swinging the stroke tool (the bat) 102, the pressure caused by the flow of the air is applied to thepitot tube 104 having an opening toward the direction of the movement, and then the pressure is detected by thepressure sensor 106. The swing speed of the stroke tool can be obtained by converting the flow of the air into the flow rate using the detection signal. InDocument 1, the form of embedding thespeed measuring device 100 in thebat 102 is adopted, wherein thepitot tube 104 is attached so as to be exposed toward the direction of the movement of the bat, and thepressure sensor 106 and apressure correction sensor 110 having the normal line of the pressure receiving surfaces of diaphragms 108, 112 directed toward the direction of the movement, atemperature sensor 114 for measuring the temperature used for temperature compensation of thepressure sensor 106 and thepressure correction sensor 110, thearithmetic section 116, and thedisplay section 118 are embedded in thebat 102.
• FIGS. 8A and 8B show a head speed measuring device according to JP-A-2008-246139 (Document 2) as a second related-art example. FIG. 8A is a diagram showing a form of use of the head speed measuring device, and FIG. 8B is a block diagram of the head speed measuring device. InDocument 2, there is disclosed a configuration of arranging a headspeed measuring device 200 so as to be able to measure the speed of thegolf head 216 when passing through the vicinity of the lowest point of the movement locus K of thegolf head 216, the headspeed measuring device 200 including amicrowave Doppler sensor 202, anamplifier 204 for amplifying the output signal from theDoppler sensor 202, acomparator 206 for comparing the signal amplified by theamplifier 204 with a reference value to thereby output a Doppler pulse, a micro-controller 208 for receiving the signal output from thecomparator 206 and obtaining the swing speed, adisplay section 210 for displaying the swing speed and so on under the control of the micro-controller 208, and aswitch group 212 connected to the micro-controller 208.
• According to the configuration described above, since the speed of thegolf head 216 of thegolf club 214, which hits the ball B, is measured by applying pulsed light with a light axis L to thegolf head 216 when passing through the vicinity of lowest point, and then obtaining the difference between the pulsed light reflected by thegolf head 216 and having the frequency varied due to the Doppler effect and the reference pulse, it is possible to measure the swing speed contactlessly with thegolf head 216.
• FIGS. 9A and 9B show a long-putting practice device according to JP-A-2006-158893 (Document 3) as a third related-art example. FIG. 9A is an overall schematic diagram, FIG. 9B is a block diagram of a unit constituting the long-putting practice device. InDocument 3, there is disclosed a long-putting practice device 300 having a thin plate-like magnet 304 with a predetermined width bonded to the bottom surface of aputter head 302 for hitting a ball, aunit 308 collectively including amagnetic sensor 310, a CPUarithmetic processing circuit 312, adisplay circuit 314, apower supply circuit 316, and so on disposed on a green simulatedmat 306, thereby detecting the speed of theputter head 302. Thus, the magnetic field generated from the thin plate-like magnet 304 moves with theputter head 302, and the speed of theputter head 302 is calculated using the time period required for the magnetic field to pass above themagnetic sensor 310. Therefore, similarly to the case ofDocument 2, the speed of theputter head 302 can be measured in a contactless manner.
• However, inDocument 1, thepressure correction sensor 110 and the correction process using it for correcting the acceleration of thebat 102 in the direction of the movement are required, which causes a problem of further increasing the number of components to increase in cost. InDocuments 2 and 3, since the measurement is performed in a contactless manner, misalignment is caused between the measurement direction and the direction in which the golf club or the putter is swung, which causes an error in the swing speed thus measured. Further, inDocument 3, there arises a problem that a variation is caused in the detected speed of theputter head 302 due to the variation in the height of the thin plate-like magnet attached to theputter head 302 when passing above themagnetic sensor 310, the variation in the height depending on the skill of the player.
SUMMARY
• An advantage of some aspects of the invention is to provide a speed detector with a suppressed variation in measurement while achieving a simple configuration, and a SWING tool equipped with the speed detector.
• The invention can solve at least a part of the problem described above, and can be embodied as the following application examples.
APPLICATION EXAMPLE 1
• According to this application example of the invention, there is provided a speed detector including a pressure sensor including a pitot tube attached to a moving body in a state in which an air inlet hole is directed toward a direction of a movement of the moving body, a diaphragm having a pressure receiving surface displaced by the pressure, and a pressure-sensitive section adapted to receive force caused by the displacement to detect the pressure, the pressure sensor being disposed to the moving body and detecting the pressure caused in the pitot tube, and an operation section adapted to detect a speed of the moving body based on the difference between the pressure at rest and the pressure in movement of the moving body, wherein the pressure sensor is disposed so that a normal line of the pressure receiving surface becomes perpendicular to the direction of the movement.
• According to the configuration described above, since the speed of the moving body can be detected by a single pressure sensor, and at the same time, the normal line of the pressure receiving surface of the diaphragm is arranged to be perpendicular to the direction of the movement of the moving body, even if the acceleration occurs in the direction of the movement, no displacement of the pressure receiving surface is caused by the acceleration, and therefore, the pressure sensor can be prevented from falsely detecting the acceleration in the direction of the movement as the pressure.
APPLICATION EXAMPLE 2
• According to this application example of the invention, there is provided a speed detector including a container attached to a moving body and having an opening section, a first pressure sensor disposed inside the container and including a pitot tube attached to the opening section in the state of having an air inlet hole directed toward a direction of a movement of the moving body to form an internal space integrally with the container, and having pressure in the internal space vary due to the movement of the moving body, a diaphragm having a pressure receiving surface displaced by the pressure, and a pressure-sensitive section adapted to receive force caused by the displacement to detect the pressure, a second pressure sensor disposed outside the internal space, and a second operation section adapted to detect a speed of the moving body based on a difference between the pressure detected by the first pressure sensor and the pressure detected by the second pressure sensor, wherein the first and the second pressure sensors are disposed so that a normal line of the pressure receiving surface becomes perpendicular to the direction of the movement.
• According to the configuration described above, it results that the pressure ((static pressure)+(dynamic pressure)) measured by the first pressure sensor and the pressure (static pressure) measured by the second pressure sensor are calculated simultaneously to calculate the dynamic pressure based on the difference between the both parties, and the speed of the moving body is obtained based on the dynamic pressure thus obtained. Therefore, the speed of the moving body can be measured without previously measuring the static pressure.
APPLICATION EXAMPLE 3
• According to this application example of the invention, in the speed detector of Application Example 1 or 2 of the invention, the pitot tube has a tapered shape having a diameter decreasing toward the direction of the movement.
• According to the configuration described above, the turbulent flow of the air due to the pitot tube can be prevented outside the pitot tube to thereby reduce the interference to the movement of the moving body.
APPLICATION EXAMPLE 4
• According to this application example of the invention, in the speed detector of either one of Application Examples 1 to 3 of the invention, the moving body receives acceleration in a direction perpendicular to the direction of the movement, and the pressure sensor is disposed so that the normal line of the pressure receiving surface becomes perpendicular to the direction of the acceleration.
• As the movement of receiving the acceleration in the direction perpendicular to the direction of the movement of the moving body, a circular movement can be cited, for example. Therefore, according to the configuration described above, it becomes possible to prevent the false detection of the acceleration caused when the moving body performs the circular movement as the pressure to thereby measure the speed of the moving body with high accuracy.
APPLICATION EXAMPLE 5
• According to this application example of the invention, in the speed detector of any one of Application Examples 1, 3 and 4 of the invention, the moving body stops at a measured point for a predetermined period of time, and then moves so as to pass through the measured point, and the operation section calculates the speed of the moving body based on a difference between the pressure the pressure sensor detects when the moving body stops at the measured point for the predetermined period of time, and the pressure the pressure sensor detects when the moving body is in movement.
• In the configuration described above, the pressure sensor detects only the static pressure when the moving body is at rest, while it detects the sum of the static pressure and the dynamic pressure when the moving body is in movement. Further, the pressure measured by the pressure sensor has the value varying in accordance with the atmospheric pressure when the heightwise position of the pressure sensor varies. However, the static pressure is equal as long as the moving body stays at the same height. Therefore, if the difference between the pressure in movement and the pressure at rest of the moving body is calculated at the measured point, the component of the dynamic pressure of the moving body can be extracted, and thus the speed of the moving body can be obtained. For example, in the case in which the speed of the moving body becomes the highest, the peak value of the pressure the pressure sensor detects is detected, and the difference between the peak value and the pressure value at rest is calculated, thereby obtaining the speed of the moving body. Further, in the case in which the ball is disposed at the measured point, the pressure value the pressure sensor detects at the moment the moving body actually hit the ball becomes discontinuous. Therefore, by calculating the difference between the pressure value at a time point prior to the moment the pressure becomes discontinuous and the pressure at rest described above, the speed of the moving body can be obtained.
APPLICATION EXAMPLE 6
• According to this application example of the invention, there is provided a SWING tool having the speed detector according to any one of Application Examples 1 to 5 of the invention attached.
• According to the configuration described above, the SWING tool capable of calculating the speed of the moving body without being affected by the acceleration acting on the moving body.
BRIEF DESCRIPTION OF THE DRAWINGS
• The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.
• FIGS. 1A through 1C are schematic diagrams showing a speed detector and a SWING tool attached with the speed detector according to a first embodiment, whereinFIG. 1A is a schematic diagram showing the case in which the speed detector attached to the SWING tool,FIG. 1B is a schematic diagram showing an internal configuration of the speed detector, andFIG. 1C is a cross-sectional view of a pressure sensor constituting the speed detector.
• FIGS. 2A and 2B are schematic diagrams showing the speed detector and the SWING tool attached with the speed detector according to the first embodiment, whereinFIG. 2A is a schematic diagram of a stroke tool attached with the speed detector viewed from the direction of the movement, andFIG. 2B is a partial detail diagram of the area surrounded by a broken line shown inFIG. 2A, and at the same time a cross-sectional diagram along the line A-A′ shown inFIG. 1A.
• FIG. 3 is a diagram showing the acceleration acting on a diaphragm.
• FIGS. 4A through 4C are diagrams showing a procedure of converting an oscillation frequency into pressure in an operation section of the first embodiment, whereinFIG. 4A is a table showing relationships (at measuring temperature of 30° C.) between the pressure, the frequency, and a normalized frequency,FIG. 4B is a plot chart showing the relationship between the pressure and the frequency, andFIG. 4C is a chart showing dots representing the relationship between the pressure and the frequency fitted with a polynomial expression.
• FIGS. 5A and 5B are graphs showing the pressure and the speed of the moving body calculated and then displayed by the operation section of the first embodiment, whereinFIG. 5A is a graph showing the pressure measured in theoperation section28, andFIG. 5B is a graph showing the speed of the moving body (agolf head12d) calculated based on the pressure thus measured.
• FIG. 6 is a schematic diagram of a speed detector according to a second embodiment.
• FIGS. 7A and 7B are schematic diagrams of a speed measuring device according to a first related art example, whereinFIG. 7A is a diagram showing a form of use of the speed measuring device, andFIG. 7B is a detail diagram of the speed measuring device.
• FIGS. 8A and 8B are schematic diagrams of a head speed measuring device according to a second related art example, whereinFIG. 8A is a diagram showing a form of use of the head speed measuring device, andFIG. 83 is a block diagram of the head speed measuring device.
• FIGS. 9A and 93 are schematic diagrams of a long-putting practice device according to a third related art example, whereinFIG. 9A is an overall schematic diagram, andFIG. 9B is a block diagram of a unit constituting the long-putting practice device.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
• Hereinafter, preferred embodiments of the invention illustrated in the accompanying drawings will be explained in detail. It should be noted that constituents, types, combinations, shapes, relative arrangements thereof, and so on described in the present embodiment are not intended to limit the scope of the invention only thereto and nothing more than mere explanatory examples unless specifically described.
• FIGS. 1A through 1C,2A, and2B show a speed detector and a SWING tool attached with the speed detector according to the first embodiment.FIG. 1A is a schematic diagram of the case in which the speed detector is attached to a golf club as the SWING tool,FIG. 1B is a schematic diagram showing an internal configuration of the speed detector,FIG. 1C is a cross-sectional view of a pressure sensor constituting the speed detector,FIG. 2A is a schematic diagram of the golf club attached with the speed detector viewed from the direction of the movement, andFIG. 2B is a partial detail diagram of the area surrounded by the broken line shown inFIG. 2A, and at the same time a cross-sectional diagram along the line A-A′ shown inFIG. 1A. The speed detector according to the first embodiment has apressure sensor20 provided with apitot tube16 attached to a moving body (agolf head12d) in the state in which anair inlet hole16ais directed to toward the direction of the movement of the moving body, a diaphragm24 having a pressure receiving surface24adisplaced by the pressure, and a pressure-sensitive section26 for receiving the force due to the displacement to detect the pressure, and disposed in the moving body to detect the pressure generated in thepitot tube16, and anoperation section28 for detecting the speed of the moving body based on the difference between the pressure when the moving body stops and the pressure when the moving body is moving, wherein thepressure sensor20 is arranged so that thenormal line24bof the pressure receiving surface24abecomes perpendicular to the direction of the movement.
• Further, the moving body (thegolf head12d) moves so that the acceleration (centrifugal force) in the direction perpendicular to the direction of the movement acts on the moving body, and at the same time, thepressure sensor20 is arranged so that thenormal line24bof the pressure receiving surface24abecomes perpendicular to the direction of the acceleration.
• Further, the moving body constitutes a striking section (agolf head12d) of the SWING tool (the golf club12), which rests at the lowest point for a predetermined period of time and is then swung so as to pass through the lowest point, and theoperation section28 calculates the speed of the moving body based on the difference between the pressure thepressure sensor20 detects when the moving body rests at the lowest point for a predetermined period of time and the pressure at a characteristic point thepressure sensor20 detects while the moving body is moving.
• Hereinafter, description will be provided assuming that the SWING tool to be attached with thespeed detector10 according to the present embodiment is thegolf club12. Therefore, it is assumed in the present embodiment that the moving body is thegolf head12das the striking section of thegolf club12 for a ball, andspeed detector10 according to the present embodiment is attached to an upper part thereof.
• As shown inFIGS. 1A through 1C, thespeed detector10 according to the first embodiment has acontainer14 attached to thegolf head12d, thepitot tube16 attached to thecontainer14, and apressure sensor20 installed in thecontainer14, and further has theoperation section28 for calculating the speed of thegolf head12dexternally.
• Thepitot tube16 has a hollow shape, and has anair inlet hole16aat the tip thereof. Further, the other end thereof on the opposite side to the tip in the longitudinal direction is connected to anopening section14a. Therefore, thepitot tube16 is attached to thegolf head12dvia thecontainer14. Further, thepitot tube16 and thecontainer14 integrally form an internal space18, and as a result the pressure of the internal space18 varies in accordance with the dynamic pressure of the air (at a relative speed V₁) flowing into theair inlet hole16adue to the movement of the pitot tube.
• Now, denoting the pressure of the internal space when the relative speed of the air flowing into theair inlet hole16aof thepitot tube16 is V₁as P₁, the pressure thereof when the relative speed is V₂as P₂, and the density of the air as ρ, the following relationship is satisfied from the Bernoulli's theorem.
• $\frac{{\mathrm{<figure-callout\; label="V"\; filenames="US20110081981A1-20110407-D00005.png"\; state="\{\{state\}\}">V</figure-callout>}}_1^2}{2}+\frac{{\mathrm{<figure-callout\; label="P"\; filenames="US20110081981A1-20110407-D00005.png"\; state="\{\{state\}\}">P</figure-callout>}}_1}{\rho }=\frac{{\mathrm{<figure-callout\; label="V"\; filenames="US20110081981A1-20110407-D00003.png,US20110081981A1-20110407-D00005.png"\; state="\{\{state\}\}">V</figure-callout>}}_2^2}{2}+\frac{{\mathrm{<figure-callout\; label="P"\; filenames="US20110081981A1-20110407-D00003.png,US20110081981A1-20110407-D00005.png"\; state="\{\{state\}\}">P</figure-callout>}}_2}{\rho }$
• In the present embodiment, the speed of thegolf head12dis calculated using the pressure thepressure sensor20 detects when thegolf head12drests and the pressure the pressure sensor detects while thegolf head12dis moving. Therefore, denoting the relative speed of the air while thegolf head12dis moving as V₁, and the relative speed of the air during rest as V₂, and assuming that the relative speed V₂is equal to zero, the relative speed V₁can be obtained as follows.
• ${\mathrm{<figure-callout\; label="V"\; filenames="US20110081981A1-20110407-D00005.png"\; state="\{\{state\}\}">V</figure-callout>}}_1=k\sqrt{\frac{2\left(P_1-P_2\right)}{\rho }}$
• Here, “k” denotes a pitot tube coefficient, which is a factor depending on the mounting angle and the shape. Therefore, the pressure difference P1-P2 becomes dynamic pressure, and by calculating the pressure difference, the speed of thegolf head12dcan be obtained.
• Further, in the present embodiment, thepitot tube16 is formed to have a tapered shape tapering toward the direction (direction of the swing) of the movement of thegolf head12d. Thus, it becomes possible to prevent the turbulent flow of the air due to the movement of thepitot tube16 from occurring to thereby reduce the interference to the movement of thegolf head12d.
• As shown inFIG. 1C, thepressure sensor20 has a housing22, a diaphragm24 forming a part of the housing22 and having a pressure receiving surface displaced in accordance with the pressure, and the pressure-sensitive section26 disposed inside the housing22 and for receiving the force due to the displacement of the pressure receiving surface24aof the diaphragm24 to thereby detect the pressure, and has the housing22 be airtightly sealed to form a vacuum therein to thereby measure absolute pressure based on vacuum.
• Flexural deformation inward of the housing22 is caused by the external pressure in the pressure receiving surface24aof the diaphragm24. Further, inside the diaphragm24 there are disposed a pair ofsupport sections24c.
• The pressure-sensitive section26 has a vibrating arm26aof a double tuning-fork type or a single beam type, a pair ofbase sections26bcoupled to the both ends of the vibrating arm26a, and sets the detection axis for detecting the force to the direction of a line connecting the pair ofbase sections26b. Therespective base sections26bare fixed to thesupport sections24cformed inside the diaphragm24, and thus supported. Further, the vibrating arms26aare each provided with an excitation electrode (not shown), and by externally applying an alternating-current voltage to the excitation electrodes (not shown), the vibrating arm26avibrates at a predetermined resonant frequency.
• As shown inFIG. 1C, when the pressure P is applied to the diaphragm24, the flexural deformation inward of the housing22 is caused in the pressure receiving surface24ain accordance with the strength of the pressure P, and at the same time, the distance between thesupport sections24cincreases in accordance with the strength of the pressure P. Therefore, since the tensile stress F corresponding to the strength of the pressure P acts on the vibrating arm26a, the resonant frequency of the vibrating arm26arises in accordance with the strength of the pressure P. In other words, since internal stress is caused in the vibrating arm26ain accordance with the pressure thus received, and the resonant frequency varies in accordance with the internal stress, it becomes possible for thepressure sensor20 to detect the pressure, and thus measuring the pressure. It should be noted that since in the inside of thepressure sensor20 vacuum is taken as a reference, in the case in which the outside is also in a vacuum state similar to the inside of the housing22, there is no chance that pressure acts on the pressure receiving surface24aof the diaphragm24, and therefore, no internal stress occurs in the vibrating arm26a.
• Incidentally, flexural deformation is also caused in the pressure receiving surface24aof the diaphragm24 not only by pressure but also by acceleration. Since thegolf club12 as an application object of thespeed detector10 according to the present embodiment has a shape obtained by connecting agrip12a, ashaft12b, and thegolf head12din series, and the motion of swinging thegolf head12daround thegrip12ais performed, not only the acceleration in the direction of the movement but also the acceleration (centrifugal force) in the direction perpendicular to the direction of the movement act on thegolf head12d, as a result.
• Therefore, in the present embodiment, it is required to arrange thepressure sensor20 so that thenormal line24bof the pressure receiving surface24aof the diaphragm24 becomes perpendicular to the directions of the two kinds of acceleration described above. In the SWING with thegolf club12, since the acceleration (the centrifugal force) acts in the substantially longitudinal direction of theshaft12bof thegolf club12, it is required to arrange the pressure sensor so that thenormal line24bof the pressure receiving surface24abecomes perpendicular to both of the direction (the direction of the swing, +X direction inFIG. 2A) of the movement of thegolf head12dand thelongitudinal direction12cof theshaft12bas shown inFIG. 23.
• FIG. 3 shows the acceleration acting on a diaphragm24. Now, assuming thegrip12a(the portion gripped with hands) as the center O, and denoting the distance from the center O to the center position A of the diaphragm24 of thespeed detector10 attached to thegolf head12das “r,” the direction (the direction of the movement) of the swing as “θ,” and the mass of the diaphragm24 as “M,” the acceleration in the direction of the movement of thegolf head12dis expressed as M·r·d²θ/dt², and the acceleration in thelongitudinal direction12c(the r direction) of theshaft12bis expressed as M·r·(dθ/dt)². Here, in the case with thegolf club12, it is ideal that the golf ball is hit when thegolf head12dreaches the lowest point, and at the same time, the speed of thegolf head12dbecomes the maximum at the lowest point. In this case, since de/dt becomes maximum, and at the same takes an extremal value, d²θ/dt²becomes zero. Therefore, it seems that the acceleration in the direction of θ does not exist at the lowest point. However, in reality, since it result that the component in the direction (the direction of θ) of the movement of thegolf head12dappears also at the lowest point depending on the skill of the player, by disposing thepressure sensor20 as in the present embodiment, the speed thereof in the direction of θ can be obtained while preventing the acceleration component in the direction of θ from being detected.
• Theoperation section28 calculates the variation in the pressure inside the container based on the variation in the resonant frequency of the oscillation signal output from thepressure sensor20, and then calculates the speed of thegolf head12dbased on the variation in the pressure. Specifically, the speed of thegolf head12dis calculated based on the difference between the pressure thepressure sensor20 detects when thegolf head12drests for a predetermined period of time at the lowest point and the pressure at the characteristic point thepressure sensor20 detects when thegolf head12dis in movement. Here, the characteristic point denotes a time point corresponding to the maximum value (in most cases, the pressure becomes maximum at the lowest point) of the pressure measured when swinging thegolf club12, or a time point at which a discontinuous change in the pressure caused at the moment of hitting the golf ball with thegolf club12 occurs.
• Theoperation section28 is required to be electrically connected to the excitation electrode (not shown) of thepressure sensor20, but does not have any restriction on the position in the arrangement. Therefore, it is possible for theoperation section28 to be disposed outside thegolf club12, and connected to acable30, which is connected to the excitation electrode (not shown) and inserted in theshaft12band thegrip12a, for example. Further, it is assumed that theoperation section28 measures the resonant frequency every predetermined period of time, and is able to display the temporal variation thereof on the display as a graph. Further, theoperation section28 has a program configured so that the pressure can be calculated using a polynomial in the oscillation frequency thus measured and coefficients thereof. Further, the program of theoperation section28 is configured so as to calculate the dynamic pressure from the difference between the pressure ((static pressure)+(dynamic pressure)) obtained by converting the oscillation frequency when thegolf head12dis in movement and the pressure (static pressure) obtained by converting the oscillation frequency when thegolf head12dis at rest, and then calculate the speed of the golfhead using Formula 2. It should be noted that it is assumed that a temperature sensor (not shown) connected to theoperation section28 via thecable30 is disposed inside thecontainer14, and theoperation section28 has a configuration of performing temperature compensation on the oscillation frequency of the oscillation signal input from thepressure sensor20 based on the temperature data thus input.
• FIGS. 4A through 4C show relationship between the frequency of thepressure sensor20 and the pressure.FIG. 4A is a table showing relationships (at measuring temperature of 30° C.) between the pressure, the frequency, and a normalized frequency,FIG. 4B is a plot chart showing the relationship between the pressure and the frequency, andFIG. 4C is a chart showing dots representing the relationship between the pressure and the frequency fitted with a polynomial expression. The oscillation frequency of thepressure sensor20 varies in accordance with the pressure from the outside as described above. Therefore, when calculating the pressure based on the oscillation frequency in theoperation section28, the following operation is previously performed using an external PC or the like. Firstly, the oscillation frequency of thepressure sensor20 is normalized by a predetermined frequency, and the relationship between the oscillation frequency and the pressure is plotted within a pressure range assumed in thepressure sensor20. Further, as shown inFIG. 4C, denoting the variable of the frequency as x, and the variable of the pressure, which is a function of the variable x, as y, the coordinates of the polynomial expression (power series) of the oscillation frequency fitted to these points plotted thereon are calculated using simultaneous linear equations with multiple unknowns, and then the coordinates thus obtained are stored in a storage area (not shown) of theoperation section28. Thus, when measuring the oscillation frequency of the oscillation signal of thepressure sensor20, theoperation section28 can retrieve the coordinates from the storage area (not shown), and then substitutes the coordinates into the polynomial expression of the oscillation frequency, thereby obtaining the pressure.
• In the present embodiment, the pressure measured by thepressure sensor20 varies in accordance with the variation in atmospheric pressure caused by the variation in the heightwise position. Therefore, it is not achievable to measure the pressure at the lowest point of thegolf head12dat a different heightwise position. Further, it is not achievable to simultaneously measure the pressure (static pressure) when thegolf head12dis at rest at the lowest point and the pressure ((dynamic pressure)+(static pressure)) at the lowest point of thegolf head12dwhen performing the SWING with thegolf club12. Incidentally, in the procedure of the SWING with thegolf club12, thegolf head12dis stopped at the lowest point of thegolf head12d, namely the position for hitting the golf ball, for several seconds (an address operation), then thegolf head12dis taken back toward the opposite direction to the direction (the direction of the movement) in which the golf ball is hit to fly, and then thegolf head12dis swung in the direction of the movement so as to pass through the lowest point. Here, since it is possible to assume that the variation in the heightwise position hardly occurs during the period of performing the address operation, the static pressure at the lowest point can be measured at the stage of the address operation.
• Therefore, in theoperation section28 the program is configured so as to set the time point at which the oscillation frequency takes the maximum value after the player starts the swing as the time point at which thegolf head12dpasses through the lowest point, calculate the maximum value of the pressure ((dynamic pressure)+(static pressure)) in movement based on the maximum value of the oscillation frequency, extract the period of time in which the variation in the oscillation frequency stays within a predetermined range for a predetermined time of a few seconds prior to the time point, obtain the pressure at rest based on the oscillation frequency (besides the average value of the oscillation frequency in this period of time, the highest value or the lowest value can also be adopted) in this period of time, then calculate the dynamic pressure by subtracting the pressure at rest from the maximum value of the pressure in movement, and then obtain the speed of thegolf head12d(the speed detector10) based on the dynamic pressure.
• Further, the present embodiment can be used not only in the SWING with thegolf club12, but also in actually hitting the golf ball with thegolf club12. In this case, since the oscillation frequency of the oscillation signal output from thepressure sensor20 at the moment of hitting the golf ball with thegolf head12dshows discontinuous values, it is possible for theoperation section28 to extract the pressure immediately before the discontinuous value appears, and to obtain the swing speed based on the difference between the pressure thus extracted and the pressure at rest.
• FIGS. 5A and 5B show a graph representing the pressure measured by theoperation section28 and the speed of the moving body (thegolf head12d).FIG. 5A is a graph showing the pressure measured by theoperation section28, andFIG. 5B is a graph showing the speed of the moving body (thegolf head12d) obtained from the pressure thus measured. InFIGS. 5A and 5B, thegolf club12 was swung three times. As a series of operations of thegolf club12, there can be cited (1) address operation (initial position) at the lowest point, (2) take back, (3) stop at a take-back position, (4) swing passing through the lowest point, (5) stop at the end of the swing, (6) movement for returning the initial position. As shown inFIG. 5A, in the operation (1), since thegolf head12d(the speed detector10) is located at the lowest point (the initial position), thegolf head12dhas a predetermined frequency and the measured pressure corresponding thereto. Then, when taking back and the stopping thegolf head12das in the operations (2) and (3), the measured pressure is reduced since the position of thepitot tube16 is raised, and the oscillation frequency is lowered in accordance therewith. Then, by making the swing as in the operation (4), the air flows into thepitot tube16, and therefore, the dynamic pressure is added to the measured pressure of thepitot tube16 to raise the oscillation frequency, and then the measured pressure and the oscillation frequency reach respective peaks when thegolf head12dreaches the highest speed at the lowest point, and then the values of the both parties are lowered after passing the respective peaks. Then, in the operation (5), since the swing is completed, no dynamic pressure exists, and the measured pressure becomes in a low state since thepitot tube16 comes the high position similarly to the case of the operation (3), and the measured pressure returns to the state of the operation (1) by returning thegolf head12dto the lowest point in the operation (6). Since the measured pressure is obtained as described above, the speed of thegolf head12dcan be obtained as shown inFIG. 5B assuming the pressure when thegolf head12dis at rest at the lowest point as the reference pressure. It should be noted that inFIG. 5B, the right side ofFormula 2 is bracketed with a root sign, and is unable to be calculated if the measured pressure P₁takes a value lower than the reference pressure P₂, and therefore, it is calculated using the absolute value of the difference between the measured pressure and the reference pressure.
• FIG. 6 shows a speed detector according to a second embodiment. The speed detector according to the second embodiment has acontainer42 attached to the moving body and having anopening section42a, afirst pressure sensor48 disposed inside thecontainer42, provided with apitot tube44 attached to theopening section42ain the state of having anair inlet hole44adirected toward the direction of the movement of the moving body to form aninternal space46 integrally with thecontainer42, and having the pressure in theinternal space46 vary due to the movement of the moving body, a diaphragm having a pressure receiving surface displaced in accordance with the pressure, and a pressure-sensitive section for receiving the force caused by the displacement to detect the pressure, asecond pressure sensor54 disposed outside theinternal space46, and a second operation section (not shown) for detecting the speed of the moving body based on the difference between the pressure detected by thefirst pressure sensor48 and the pressure detected by thesecond pressure sensor54, and thepressure sensors48,54 are arranged so that the normal line of the pressure receiving surface becomes perpendicular to the direction of the movement.
• Thefirst pressure sensor48 and thesecond pressure sensor54 according to the second embodiment are the same as thepressure sensor20 of the first embodiment, and are attached to the moving body in the same direction. Further, similarly to thepressure sensor20 according to the first embodiment, thefirst pressure sensor48 is disposed in theinternal space46 formed of thecontainer42 and thepitot tube44, and is capable of detecting the pressure inside theinternal space46 in accordance with the speed of the air flowing into theair inlet hole44aof thepitot tube44. On the other hand, thesecond pressure sensor54 is disposed in asecond container50 disposed outside thecontainer42, and asecond pitot tube52 for measuring the static pressure is coupled to theopening section50aof thesecond container50. Thesecond pitot tube52 is formed integrally with thefirst pitot tube44, and has anair inlet hole52a. However, since thesecond pitot tube52 is further provided with aleak hole52b, the pressure in thesecond container50 is always equal to the static pressure irrespective of the speed of the air flowing into theair inlet hole52a.
• Therefore, in the second operation section (not shown), it becomes possible to measure the dynamic pressure by calculating the difference between the pressure ((dynamic pressure)+(static pressure)) obtained by converting the oscillation frequency measured by thefirst pressure sensor48 and the pressure (static pressure) obtained by converting the oscillation frequency measured by thesecond pressure sensor54. It should be noted that although the operation for converting the oscillation frequency measured into the pressure is performed also in the second operation section (not shown), since substantially the same operation as that of theoperation section28 in the first embodiment is performed, the explanation will be omitted.
• As described above, according to thespeed detector10 related to the first embodiment, firstly, since the speed of thegolf head12dcan be detected with asingle pressure sensor20, and at the same time, thenormal line24bof the pressure receiving surface24aof the diaphragm24 is arranged so as to be perpendicular to the direction of the movement of thegolf head12d, even if the acceleration in the direction of the movement is generated, the displacement of the pressure receiving surface24ais not caused by the acceleration, and therefore, thepressure sensor20 can be prevented from falsely detecting the acceleration in the direction of the movement as the pressure.
• Secondly, by adopting the configuration of the second embodiment, it results that the pressure ((static pressure)+(dynamic pressure)) measured by thefirst pressure sensor48 and the pressure (static pressure) measured by thesecond pressure sensor54 are calculated simultaneously to calculate the dynamic pressure based on the difference between the both parties, and the speed of thegolf head12dis obtained based on the dynamic pressure thus obtained. Therefore, the speed of thegolf head12dcan be measured without previously measuring the static pressure.
• Thirdly, since thepitot tubes16,44 are each formed to have a tapered shape having the diameter decreasing toward the direction of the movement of thegolf head12d, it becomes possible to prevent the turbulent flow of the air caused by thepitot tubes16,44 in the outside of thepitot tubes16,44 to thereby reduce the interference to the movement of thegolf head12d.
• Fourthly, thegolf head12dmoves so that the acceleration in the direction perpendicular to the direction of the movement acts thereon, and at the same time, the pressure sensor20 (48,54) is arranged so that thenormal line24bof the pressure receiving surface24abecomes perpendicular to the direction (the r direction) of the acceleration (centrifugal force). As the movement of receiving the acceleration in the direction perpendicular to the direction of the movement of thegolf head12d, a circular movement (swing) can be cited. Therefore, according to the configuration described above, it becomes possible to prevent the false detection of the acceleration caused when thegolf head12dperforms the circular movement as the pressure to thereby measure the speed of thegolf head12dwith high accuracy.
• Fifthly, as described in the first embodiment, theoperation section28 is arranged to have a configuration of obtaining the speed of thegolf head12dfrom the difference between the pressure thepressure sensor20 detects when the golf headrests for a predetermined period of time at the lowest point of the movement (swing) of thegolf head12d, and the pressure at the characteristic point thepressure sensor20 detects when thegolf head12dis in movement (in the swing motion).
• In the configuration described above, the characteristic point denotes the time point at which the pressure measured becomes the highest or the time point immediately before the pressure measured becomes discontinuous. The pressure measured by thepressure sensor20 has the value varying in accordance with the atmospheric pressure when the heightwise position of thepressure sensor20 varies. Further, in thegolf head12dperforming the movement described above, since the speed at the lowest point becomes the highest, it is possible for theoperation section28 to detect it as a peak value. Further, the pressure when thegolf head12dis at rest previously measured at the lowest point, and the component of the static pressure in the pressure in movement (in the swing motion) when thegolf head12dpassing through the lowest point become theoretically the same value. Therefore, according to the configuration described above, it is possible to obtain the dynamic pressure by subtracting the pressure at rest previously measured at the lowest point from the pressure in movement when thegolf head12dpassing through the lowest point, and then obtain the speed of thegolf head12dat the lowest point based on the dynamic pressure. Further, the pressure thepressure sensor20 detects at the moment thegolf head12dactually hit the ball becomes discontinuous. Therefore, by calculating the difference between the pressure at a time point prior to the moment the pressure becomes discontinuous and the pressure at rest described above, the speed of thegolf head12dcan be obtained.
• Sixthly, by configuring thegolf club12 making it possible to swing thespeed sensor10 described above attached to thegolf head12d, thegolf club12 capable of obtaining the speed of thegolf head12dwithout being affected by the acceleration acted on thegolf head12dis obtained.
• It should be noted that although the description is presented assuming that the SWING tool and the moving body to which thespeed detector10 is attached is thegolf head12din either of the embodiments, the invention is not limited thereto. It is also possible to attach thespeed detector10 to, for example, a frame or a string of a tennis racket, a baseball bat.
• Further, although in either of the embodiments, the description is presented assuming that the pressure sensor applies the piezoelectric vibrator as the pressure-sensitive section26, and detects the pressure based on the variation in the oscillation frequency of the piezoelectric vibrator due to the force applied by the diaphragm24, the invention is not limited thereto. In other words, it is obvious that any pressure sensor using the diaphragm24 such as a capacitance variation type, a piezoresistance variation type can widely be applied as the pressure-sensitive section besides the frequency variation type described above.
• The entire disclosure of Japanese Patent Application No. 2009-232872, filed Oct. 6, 2009 and Japanese Patent Application No. 2010-167783, filed Jul. 27, 2010 is expressly incorporated by reference herein.

Claims (15)

1. A speed detector comprising:

a pressure sensor including

a pitot tube attached to a moving body in a state in which an air inlet hole is directed toward a direction of a movement of the moving body,

a diaphragm having a pressure receiving surface displaced by pressure, and

a pressure-sensitive section adapted to receive force caused by the displacement to detect the pressure,

the pressure sensor being disposed to the moving body and detecting the pressure caused in the pitot tube; and

an operation section adapted to detect a speed of the moving body based on the difference between the pressure at rest and the pressure in movement of the moving body,

wherein the pressure sensor is disposed so that a normal line of the pressure receiving surface becomes perpendicular to the direction of the movement.

2. A speed detector comprising:

a container attached to a moving body and having an opening section;

a first pressure sensor disposed inside the container and including

a pitot tube attached to the opening section in the state of having an air inlet hole directed toward a direction of a movement of the moving body to form an internal space integrally with the container, and having pressure in the internal space vary due to the movement of the moving body,

a diaphragm having a pressure receiving surface displaced by the pressure, and

a pressure-sensitive section adapted to receive force caused by the displacement to detect the pressure;

a second pressure sensor disposed outside the internal space; and

a second operation section adapted to detect a speed of the moving body based on a difference between the pressure detected by the first pressure sensor and the pressure detected by the second pressure sensor,

wherein the first and the second pressure sensors are disposed so that a normal line of the pressure receiving surface becomes perpendicular to the direction of the movement.

3. The speed detector according toclaim 1, wherein

the pitot tube has a tapered shape having a diameter decreasing toward the direction of the movement.

4. The speed detector according toclaim 1, wherein

the moving body receives acceleration in a direction perpendicular to the direction of the movement, and the pressure sensor is disposed so that the normal line of the pressure receiving surface becomes perpendicular to the direction of the acceleration.

5. The speed detector according toclaim 1, wherein

the moving body stops at a measured point for a predetermined period of time, and then moves so as to pass through the measured point, and

the operation section calculates the speed of the moving body based on a difference between the pressure the pressure sensor detects when the moving body stops at the measured point for the predetermined period of time, and the pressure the pressure sensor detects when the moving body is in movement.

6. A SWING tool comprising:

the speed detector according toclaim 1 attached.

7. The speed detector according toclaim 3, wherein

the moving body receives acceleration in a direction perpendicular to the direction of the movement, and the pressure sensor is disposed so that the normal line of the pressure receiving surface becomes perpendicular to the direction of the acceleration.

8. The speed detector according toclaim 3, wherein

the moving body stops at a measured point for a predetermined period of time, and then moves so as to pass through the measured point, and

the operation section calculates the speed of the moving body based on a difference between the pressure the pressure sensor detects when the moving body stops at the measured point for the predetermined period of time, and the pressure the pressure sensor detects when the moving body is in movement.

9. The speed detector according toclaim 4, wherein

the moving body stops at a measured point for a predetermined period of time, and then moves so as to pass through the measured point, and

the operation section calculates the speed of the moving body based on a difference between the pressure the pressure sensor detects when the moving body stops at the measured point for the predetermined period of time, and the pressure the pressure sensor detects when the moving body is in movement.

10. A SWING tool comprising:

the speed detector according toclaim 3 attached.

11. A SWING tool comprising:

the speed detector according toclaim 4 attached.

12. A SWING tool comprising:

the speed detector according toclaim 5 attached.

13. A SWING tool comprising:

the speed detector according toclaim 7 attached.

14. A SWING tool comprising:

the speed detector according toclaim 8 attached.

15. A SWING tool comprising:

the speed detector according toclaim 9 attached.

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